Compensation Of Friction Forces Research Articles

Analytical friction force compensation of flow curves out of layer compression tests with the pin extrusion test

For conventional material models like Yld2000-2d or BBC05 the equi-biaxial yield strength is required for the parameter identification. In this context, a commonly used test setup is the hydraulic bulge test. However, an inaccuracy in the characterization of the initial yield strength is present in the hydraulic bulge test. Due to the evaluation of the resulting curvature of the specimen, that is nearly infinite at the onset of yielding, the calculated stress can significant vary. Another proposed test setup for the characterization of the equi-biaxial stress state is the layer compression test. Here, the onset of yielding can be characterized with sufficient accuracy. The disadvantage in this test is the friction between stack and tool that leads to an overestimation of the flow curve. Thus, robust and experimental based friction compensation should be used, to gain a comparable hardening behaviour as in the hydraulic bulge test. In this contribution, the friction in the layer compression test is compensated by characterization of the tribological conditions. Thus, the tribological system consisting of workpiece surface, tool surface and lubricant is characterized using pin extrusion tests. The friction is analysed for the two steel grades DC06 and DP600 and the aluminium AA5182. With the identified friction factors, the measured testing force in the layer compression test is reduced by the portion of friction. For verification, hydraulic bulge tests, which are approximately friction free, are performed and compared with the resulting flow curves of the layer compression tests. Results confirm, that a friction compensation of the layer compression tests lead to a significant improvement of the resulting material parameters in comparison to the hydraulic bulge tests. Additional, a new method for the friction factor characterization is presented that uses in the stress difference of flow curves characterized in hydraulic bulge tests and layer compression tests.

Improvement of Reverse Motion of an NC Moving Table Based on Vector Control Method by Friction Force Compensation

Lost motion is a phenomenon that often occurs during the motion of a moving table, which is used for machine tools to ensure their precise positioning. Lost motion occurs when the direction of the table’s motion reverses as a result of nonlinear friction characteristics between the feed drive mechanisms such as the ball screw and linear guide. Lost motion directly influences the machining accuracy of a machine tool, because the accuracy of machining depends on the relative motion between the tool and the workpiece. A number of studies have dealt with suppressing the occurrence of lost motion using model-based control. However, nonlinear friction has not been addressed to the same extent, as it is difficult to determine the motion characteristics of and therefore develop a model for the nonlinear friction. Thus, to address these problems, we propose a compensation method for revers motion based on vector control, which is used to control the torque and velocity of the alternating current (AC) servomotor in the moving table. In this study, the current applied to the AC servomotor for a vector with force components in the rotational direction (torque component) and in the direction perpendicular to the axis of rotation (field component) was measured to clarify and establish the relationship between the motion and the control current. The compensation current was then derived as a functional value based on the results of the measured torque at the occurrence of lost motion. Further, tests were carried out using the proposed method, which directly applies the drive current of the AC servomotor by using a field-programmable gate array controller to improve the reverse motion of the table. The results reveal that the motion characteristics of a numerical control (NC) table can be determined by measuring the drive current of the AC servomotor. In addition, it is verified that the proposed method can compensate for the torque command smoothly at the time of velocity reversal, resulting in suppression of the lost motion and reduction of reverse motion of the moving table.

Improvement of reversal motion by friction force compensation of NC moving table

Improvement of reversal motion by friction force compensation of NC moving table

Sensorless Force Estimation of SCARA Robot System with Friction Compensation

In this paper, the friction compensation method of SCARA robot is proposed. During the operation, the friction force in the system causes the heat to the robot and system. Since heat which occurred in the system is accumulated for a long time, the robot and system have been damaged. Moreover, performance and stability of the system have been reduced. Therefore, compensation of friction force is an important method for increase performance and stability of the system. In this paper, the disturbance observer is used with mathematic modelling of friction compensation for compensate the friction force in the system. From the simulation results, the system which has a friction force compensation can show the increasing of performance and stability.

Force Control of Human–Robot Interaction Using Twin Direct-Drive Motor System Based on Modal Space Design

Future robot systems are required to focus on developing more flexible systems for use with human operator. These robots must operate more slowly and be more compliant to safe user interaction. This paper proposes an improved design methodology for the human-robot interaction system. The main contribution of the work described in this paper is the design of dual disturbance observers combined with modal space design for the twin direct-drive motor system. Two of the same direct-drive motors are required and connected by wire rope mechanism. Since both direct-drive motors have almost the same value of the friction effect and other nonlinearities, it is easy for the proposed system to compensate these deterioration effects. The proposed force control system is independently controlled in acceleration dimension by realizing the system based on common mode and differential mode. In the common mode, it is utilized for control of vibration suppression and wire rope tension. Moreover, the bandwidth and the stiffness of mechanism can be regulated by changing the wire rope tension control. In the differential mode, the purity of human external force with compensation of friction force is obtained. This mode is useful for control of the interaction force of human. The effectiveness of the proposed method is verified by experimental results.

Discrete-Time Elasto-Plastic Friction Estimation

For control applications involving small displacements and velocities, friction modeling and compensation can be very important, especially around velocity reversal. We previously described single-state friction models that are based on elasto-plastic presliding, something that reduces drift while preserving the favorable properties of existing models (e.g., dissipativity) and that provide a comparable match to experimental data. In this paper, for this class of models, discrete estimation for friction force compensation is derived. The estimator uses only position and velocity (not force) measurements and integrates over space rather than time, yielding a discrete-time implementation that is robust to issues of sample size and sensor noise, reliably renders static friction and is computationally efficient for real-time implementation. Boundedness with respect to all inputs, convergence during steady sliding and dissipativity are established for the discrete-time formulation.

Adaptive Compensation of Friction Forces with Differential Filter

In this paper, we design an adaptive controller to compensate the nonlinear friction model when the output is the position. First, we present an adaptive differential filter to estimate the velocity. Secondly, the dynamic friction force is compensated by a fuzzy adaptive controller with position measurements. Finally, a simulation result for the proposed controller is demonstrated.

Accurate motion control of xy high-speed linear drives using friction model feedforward and cutting forces estimation

Accurate motion control is essential for machine tools. Both friction forces and cutting forces contribute to position and contour tracking errors. This paper presents a feedforward friction force compensation based on the Generalized Maxwell-slip (GMS) friction model that describes friction behaviour both in pre-sliding and sliding regime. An inverse-model-based disturbance observer is added to further improve the friction compensation. This disturbance observer is able to only partly reduce the effects of cutting forces. An almost complete elimination of these effects is obtained by adding a repetitive controller (RC). Experimental validations of these approaches on a linear-motor-based xy table are presented.

転がり案内における速度反転時の非線形摩擦挙動

This paper presents a new dynamic model of nonlinear friction in a ball guide way. This model includes Coulomb friction, viscous friction, Stribeck effect and nonlinear behavior of elastic deformation. By the proposed model contrary to the conventional one, the motion is not decelerated but accelerated by the elastic recovery force just after the direction is reversed This model is not symmetrical for the zero speed of motion. In our simulations the friction models of the proposed and conventional were tuned using Generic Algorithm and by applying these models the driving forces for the same reversed motion were also estimated. These simulations indicated the proposed model is much more accurate than the conventional one. The friction force compensation experiments considering the proposed model were carried out by using a linear slider for a motion in which the velocity was reversed. The tracking error was reduced to less than a half of that without compensation.

Parametrization and adaptive compensation of friction forces

This paper considers adaptive controls of systems containing non-smooth non-linear friction forces. The idea is to divide the unknown friction force into two parts so that it can be parametrized by a model linear in parameters. Then linear adaptive techniques apply. © 1997 by John Wiley & Sons, Ltd.

Fuzzy control of an inverted pendulum with fuzzy compensation of friction forces†

Abstract The purpose of this paper is to compare the stabilization, with friction compensation, of an unstable mechanical system, an inverted pendulum, by two methods: the state feedback method, which belongs to the mathematical model-based approach, and fuzzy control. In both cases, the friction forces are compensated either by a simple method, the switching of a constant threshold, or a more sophisticated one: a disturbance observer in the model-based approach and a fuzzy compensator in the fuzzy control situation. The results obtained with the latter are comparable with or even better than those obtained with the former.